1. Field of the Invention
The present invention relates to an arrangement for transporting air with the aid of a so-called electric ion or corona wind, and preferably cleansing the air at the same time.
2. The Prior Art
It is known that air can be transported with the aid of a so-called electric ion wind or corona wind. In principle, such an arrangement comprises a corona electrode and a target electrode which are mutually spaced apart and each of which is connected to a respective terminal of a d.c. voltage source, the configuration of the corona electrode and the potential difference and also the distance between the corona electrode and the target electrode being such as to generate at the corona electrode a corona discharge which produces air ions. These air ions migrate rapidly to the target electrode, under the influence of the electric field between the corona electrode and target electrode, and give their electric charge to the target electrode. During their movement towards the target electrode, the ions collide with electrically neutral air molecules, thereby also transferring the electrostatic forces to these latter molecules, so that they are also entrained towards the target electrode, thereby establishing air transportation in the form of a so-called ion or corona wind. Air transporting arrangements of this kind are found described, for instance, in international patent application PCT/SE85/00538.
When the air contains contaminant aerosols, i.e. suspended solid particles or liquid droplets, these contaminants will be charged electrically by the air ions generated by the corona discharge, and hence the contaminants, or impurities, can be precipitated electrostatically on the target electrode, provided that the electrode is suitably configured, or in a capacitor separator located downstream of the target electrode. Thus, it is possible in principle to provide an air cleansing arrangement with which air can be transported through the arrangement and contaminant aerosols extracted from the air with the aid of the air ions produced by a corona discharge.
The ability to produce in practice such an arrangement which will satisfy the requirements desired thereof, such as large volumetric air throughflows, high cleansing ability, small dimensions, reasonable potential difference between corona electrode and target electrode, and therewith reasonable high voltage levels, and a corona current which has an acceptable value with regard to the harmful gases generated by the corona discharge, particularly ozone and oxides of nitrogen, has been found to be associated, however, with several not-readily solved and closely related problems. Consequently, an arrangement of this kind which can be used in practice is not yet available commercially.
As disclosed in the aforesaid international patent application, it is possible to achieve both significant air-flow speeds and considerable volumetric air through-flows with the aid of a corona current which is acceptable with regard to the generation of ozone and other harmful gases, when the corona electrode and target electrode are located at a considerable distance apart and the corona electrode is screened effectively, so that the product of ion current and ion-migration distance in an upstream direction away from the corona electrode is negligibly small. An increase in the distance between corona electrode and target electrode, however, requires an increase in the potential difference between corona electrode and target electrode, in order to ignite the corona electrode effectively. The consequence hereof is an increase in high voltage levels of the corona electrode and/or target electrode, which in turn results in insulating and spark-over problems. In addition hereto, the need to prevent unintentional touching of the high-voltage electrodes is also increased. When the corona electrode and target electrode are spaced axially from one another in a straight air flow duct or passageway, which is primarily the most natural arrangement, it has been found that the air flow has a marked tendency to concentrate in the central part of the duct. This applies even when the target electrode is located as close to the walls of the duct as possible. Therefore, the requirement for a large volumetric air throughflow requires a flow duct of wide area, and consequently the arrangement must be given large dimensions. Furthermore, when the target electrode is placed adjacent the duct walls it is necessary to insulate the inner surfaces of the walls electrically. It has been found, however, that when the arrangement is in operation the electrically insulated wall surfaces obtain an electrostatic charge which disturbs the corona discharge and the corona electrode in a troublesome manner, preventing the electrode from igniting in the manner intended. Furthermore, positioning of the target electrodes adjacent the duct walls means, in conjunction with the essentially laminar flow of the air in the air flow duct, that the path along which the electrically charged aerosol contaminants have to migrate to the target electrode surfaces becomes relatively long, and hence the extent to which the air is cleansed is relatively low. In principle, it is possible to obtain an improvement in this regard by increasing the axial lengths of the target electrode surfaces, or primarily by using either a large number of mutually parallel and less widely spaced target electrode surfaces with intermediate electrode surfaces of opposite polarity, or a conventional capacitor separator downstream of the target electrode in the air-flow channel. All of these solutions, however, require a substantial increase in the total dimensions of the arrangement and, from the aspect of achieving the most effective cleansing effect, the two last mentioned solutions also result in a substantial increase in flow resistance in the duct. This increased flow resistance must, in turn, be compensated for by increasing the corona current and/or the distance between corona electrode and target electrode, an increase in corona current resulting in an increase in the amount of ozone and other harmful gases generated, and both solutions also requiring a greater potential difference between the electrodes. Consequently, it has been found very difficult to provide with an arrangement of this kind a satisfactory air transporting apparatus which will simultaneously cleanse the air transported, when air transportation is effected with the aid of an electric corona-wind or ion wind.
The object of the present invention is therefore to provide to this end an arrangement which is not encumbered with the aforementioned problems, or with which these problems are at least greatly reduced, and to provide an arrangement which will fulfill the aforesaid requirements in a satisfactory manner.
It has surprisingly been found that this object is achieved by means of an arrangement constructed in accordance with the following claims.